Disc galaxies with multiple triaxial structures. I. BVRI and Hα surface photometry.

We present a BVRI survey of 36 galaxies selected as candidates for having a misaligned secondary bar or a triaxial bulge inside the primary bar. Fifteen galaxies have also been observed in Hα. A positive detection of more than one triaxial structure has been found in 22 galaxies shared out as follows: 13 double-barred galaxies, 3 triple-barred galaxies, 3 double-barred galaxies with an additional structure with twisted isophotes, and 3 galaxies with a bar and a structure with twisted isophotes. Triaxial deformation(s) have been found in 6 galaxies classified as unbarred in RC3. The number of Seyfert nuclei amongst double-barred systems is high (6 over 13).